This invention relates to flow cytometry and more particularly to flow cytometry methods utilizing a mass sensor.
Flow cytometers (FCM) for enumerating the absolute levels of cells and their subsets are used extensively for blood and other clinical samples and show promise for identifying pathogenic bacteria. Flow cytometry is a mature technology that uses hydrodynamics to focus a stream of aligned and single-file particles, optics to illuminate a particle with lasers or other light sources, and detectors to resolve scattered light as well as, in some embodiments, fluorescent signals. Specificity to a target subset of cells is achieved by attaching fluorescent labels to the subset with affinity molecules such as antibodies. For many applications, the FCM functions as a highly automated fluorescent microscope. Typical FCM's cost in the range of $40,000 to $150,000. Even the most compact and economical FCM on the market today is still considered a bench top instrument and costs approximately twenty thousand dollars. A significant portion of the cost to build FCMs is directed toward the optical readout.
Another class of flow cytometers is the Coulter Counter (CC). By measuring electrical impedance through an aperture, the Coulter Counter can measure cell count and volume. Coulter Counters are used routinely as hematological analyzers for red and white blood cells. Other applications include cell biology, food analysis, cosmetics, metals, marine biology, etc.
A major clinical application for flow cytometry is staging HIV-infected patients by counting CD4+ T lymphocytes. This counting provides information about how far patients have progressed along the HTV disease course and is crucial for determining when to start or change antiretroviral therapy. Recently, two relatively cheaper, simpler and more robust CD4+ cell counting approaches have been evaluated. One approach is known as Cytospheres (Beckman Coulter), in which monoclonal antibody-coated latex spheres bind to cell expressing CD4 surface antigen. In another known approach, an automated two parameter FCM (CyFlow from Partec) is used in a volumetric protocol to count CD4+ cells that are marked with a single monoclonal fluorochrome-conjugated antibody in a known volume of blood. An erythrocyte lysing procedure is not required.